[0001] The present invention relates to methods of using radiation to pattern an electrode
of an organic electronic device and to substrates for and processed by these methods.
A preferred embodiment relates to a method of using laser radiation to isolate organic
pixel electrodes on top of a multilayer device structure containing an array of active
electronic devices such that the underlying layers are substantially unharmed and
substantially no debris is generated.
[0002] Backplanes for active matrix displays comprise an array of transistors that are individually
addressed by interconnect lines perpendicular to an array of data lines. By driving
both the interconnect lines and the data lines, a pixel pad or electrode is charged
and a portion of the display medium above this pixel electrode will switch.
[0003] One problem that is shared between conventional thin film transistor (TFT) technology
and organic semiconductor-based printed TFTs alike is the limited display area, in
which the thin film transistor, the gate line, the pixel capacitor and the pixel itself
compete with each other for space. This can lead to a reduction in the aperture ratio
and therefore the quality of the display. The aperture ratio of the display is defined
by the area of the pixel electrode divided by the area of the pixel footprint. Since
the pixel electrode is competing with the TFT, interconnects and pixel capacitor for
space in the pixel footprint, it is preferable to use a multi-level structure where
the pixel electrode is defined on a different layer from the gate interconnect and
data lines. When fabricating such an electrode it is advantageous to use an organic
conductor because it can be processed from solution, which allows for low cost deposition
techniques.
[0004] In a conventional display the silicon TFT source-drain electrodes, addressing lines
and the pixel electrodes are on one metal level of the device, and the gate electrodes
and gate addressing lines are on a second metal level of the device. In conventional
display architectures, printed electrodes and printed pixel capacitors tend to be
large and result in active matrix displays with low aperture ratios.
[0005] In our preferred structure, disclosed in patent number
PCT/GB20041000433 (
WO2004/070466), a method is provided for producing a thin film transistor device incorporating
a three-metal-level architecture resulting in a high aperture ratio and allowing for
a large pixel capacitor. The device is formed by methods of solution processing and
direct printing.
[0006] We here describe a method for patterning the upper pixel electrode on top of a multi-level
pixel structure without significant degradation of the underlying layers of the TFTs.
[0007] In the prior art, it is known that conductive inks are able to be patterned using
a wide variety of printing techniques such as ink-jet printing, screen printing, and
offset printing to produce pixel electrodes or pads. However, these are relatively
low resolution techniques that rely heavily on the wetting properties of the printing
surface.
[0008] Conductive pads can also be directly deposited on top of a multilayer stack using
a laser induced forward transfer process. This process can be executed with an infrared
laser in which case it is known as a thermal transfer process. Conducting polymer
pads have been thermal transferred onto flexible substrates as explained by
G.B. Blanchet et al in Applied Physics Letters 82(3) 2003 page 463. However, this process uses a transfer layer that would need to disposed of after
it is used, and it is unlikely that laser transferred conductive material would fill
the via hole which would be required for it to act as a pixel electrode.
[0009] It is known to use ultraviolet laser radiation for patterning; this is described
in
US20030092267A1. This teaches the use of ultraviolet laser radiation, which is absorbed by most polymer
layers and could cause detrimental effects to the performance of the TFT's. Further
background prior art can be found in
WO 2004/036663, and
US 2002/110 673.
[0010] The prior art discussed above has many drawbacks. When laser ablation is applied
to patterning of conducting layers on a substrate that already contains active electronic
devices such as TFTs, diodes, or other semiconducting devices or active layers, the
performance of these devices / layers is degraded when the laser ablation occurs close
to or in upper layers of the electronic devices. This is particularly problematic
with many organic semiconductor devices. Many molecular or conjugated polymer semiconductors
exhibit degradation effects, such as a reduction of charge carrier mobility or generation
of electronic defect states, when exposed to strong ultraviolet radiation. Using ultraviolet
radiation as described in the prior art for top level patterning for multilayer polymer
stacks will tend to cause damage of underlying layers. In addition, such ultraviolet
radiation patterning has been shown to produce debris. The formation of debris can
cause poor contact with the display medium and may lead to shorts between conductive
pads.
[0011] A method is therefore needed to define and isolate organic electrodes on top of a
multi-level polymer stack within a device without harming the underlying layers or
producing excess debris.
[0012] The present invention aims to provide an improved method for defining organic pixel
electrodes on multi-level structures using a laser ablation type process. Embodiments
have been shown to leave the underlying layers substantially unharmed and produce
substantially no excess debris.
[0013] To address the problems outlined above we describe arrangements in which the layers
in the polymer stack and the laser radiation are selected such that the radiation
is absorbed by an underlying layer that is between the organic electrode and the layers
critical to the TFT. This removes conductive material in the regions that have been
exposed to the radiation, therefore dividing the layer of conductive material into
pixel electrode pads and isolating the devices.
[0014] According to a first aspect of the present invention there is provided a method as
set out in claim 1.
[0015] Preferred features of the invention are set out in the dependent claims.
[0016] The light absorbing material may comprise a dye, either in a separate layer or within
a layer of dielectric material or the layer of conducting material, or either or both
of the layer of dielectric material or the layer of conducting material may be selected
to provide light absorption. Preferably the light absorbing material has an absorption
at a laser wavelength and the substrate is irradiated at the laser wavelength. In
some embodiments the laser wavelength is an infrared wavelength to reduce the risk
of damage to the underlying organic electronic device. This wavelength may be selected
so as not to be substantially absorbed by the organic electronic device or, more particularly,
by functional layers within this device. In other embodiments ultraviolet light is
employed. Preferably the dielectric material comprises a polymer dielectric. Preferably
the dielectric material has a thickness of greater than 1 micron, more preferably
greater than 3 microns.
[0017] Optionally a wetting surface may be included underneath the layer of conducting material,
for improved adhesion of the conducting material; this may be provided by an additional
wetting layer. Alternatively a de-wetting surface may be provided under the conducting
material, optionally by an additional, de-wetting layer, so that when the conducting
material and/or light absorbing material is heated by irradiation it melts and de-wets
to provide a gap in the conducting layer.
[0018] The conducting layer preferably forms part of an electrode for a passive or active
organic electronic device or an electrode line or interconnect such as a pixel electrode
connection or a display. In some embodiments the conductor comprises an organic conductor,
more particularly a conducting polymer such as PEDOT/PSS. However in other embodiments
the conducting material may comprise an inorganic metal film. In some preferred embodiments
the insulator has a relatively low thermal conductivity to further reduce the risk
of damage to underlying layers. Such a pixel electrode may be electrically connected
to an electrode of an underlying thin film transistor by a via hole connection.
[0019] Also disclosed is a substrate configured for conductive layer patterning using light,
after irradiation of portions of the substrate, the substrate comprising: an organic
electronic structure ; a layer of dielectric material over said electronic device;
and a layer of conducting material over said layer of dielectric material; and wherein
the substrate further includes a light absorbing material over said organic electronic
structure and under an upper surface of said layer of conducting material; characterised
in that said conducting material is substantially absent from said irradiated substrate
portions, and wherein a quantity of said light absorbing material in said irradiated
substrate portions is reduced compared to un-irradiated substrate portions.
[0020] The light absorbing material may be provided in said dielectric layer, or in a separate
layer under the conducting layer.
[0021] Preferably when irradiated from a side closest to the layer of conducting material
(i.e. from above) by light, for example at a laser wavelength, the irradiating light
is more strongly absorbed by the light absorbing material than by the organic electronic
device.
[0022] Also disclosed is a substrate as described above after irradiation of portions of
the substrate at the laser wavelength, so that conducting material is substantially
absent from irradiated substrate portions. Generally the light absorbing material
in the irradiated substrate portions is also absent, or at least reduced compared
to un-irradiated substrate portions.
[0023] According to a first class of embodiments of the present invention a method is provided
for producing a pixel electrode which is defined by the isolation of conductive electrode
pads on a polymer surface. A layered substrate is provided on which an insulating
dielectric layer is deposited on top of the active electronic devices. This is followed
by the deposition of a light absorbing layer. An absorbing dye moiety may be added
to the light absorbing layer to increase its optical density at the wavelength of
laser light. Preferably, the light absorbing layer has an optical density exceeding
0.3 - 0.5 at the laser wavelength. A wetting layer may also be deposited to improve
the wetting and adhesion of the conductive material subsequently deposited on top.
The wetting layer may also be provided by the light absorbing layer. The layered stack
is then irradiated by a laser beam such that the absorbing layer underlying the conductive
layer melts or ablates away. This step removes the conductive pathway between two
adjacent electrode pads resulting in the patterning of the conductive layer to produce
pixel electrodes and isolated devices.
[0024] It is desirable that the laser light is absorbed primarily in the light absorbing
layer, but not in any of the sensitive functional layers of the active electronic
devices. This can be substantially achieved by selecting the wavelength of the laser
to be in a spectral range in which the sensitive functional layers of the active electronic
devices are essentially transparent. Furthermore, the laser light is preferably incident
from the surface of the device, such that it is strongly attenuated before it passes
through the layers of the active electronic devices. In this way, the method inhibits
degradation of the underlying active layers of the electronic device even if the laser
is patterning directly on top of the active electronic device. It also inhibits production
of debris on the surface of the patterned conductive layer.
[0025] Any laser wavelength may be employed, and since intense light of tunable lasers are
available for the uv, visible or ir parts of the spectrum, intense light of any wavelengths
may be used.
[0026] However preferably the laser is of infrared (ir) wavelength, such as 830 nm or 1064
nm. The use of infrared light further minimizes the degradation of the underlying
layers, as low-energy infrared light is less likely to induce photochemical changes
in any of the active layers of the electronic device.
[0027] Embodiments of the method are also applicable to laser patterning in the visible
and ultraviolet spectral range provided that care is taken to reduce the leakage of
light to the active layers underneath the conducting layer, for example by giving
consideration to this when selecting the light absorbing material.
[0028] According to a second class of embodiments of the present invention a method is provided
for producing a pixel electrode which is defined by the isolation of conductive electrode
pads on a polymer surface. A layered substrate is provided on which an insulating,
dielectric layer is deposited on top of the active electronic device. This is followed
by the deposition of a light absorbing conductive layer. An absorbing dye moiety may
be added to the light absorbing conductive layer to increase its optical density at
the wavelength of laser light. Preferably, the light absorbing layer has an optical
density exceeding 0.3 - 0.5 at the laser wavelength. A wetting layer may also be deposited
to improve the wetting and adhesion of the light absorbing conductive layer on top
of the dielectric layer. The layered stack is then irradiated by a laser beam such
that the light absorbing conductive layer melts or ablates away. This step removes
the conductive pathway between two adjacent electrode pads resulting in the patterning
of the conductive layer to produce pixel electrodes and isolated devices. Since the
laser light is absorbed primarily in the light absorbing conductive layer, the method
inhibits degradation of the underlying active electronic device even if the laser
is patterning directly on top of the active electronic devices. It also inhibits debris
on the surface of the patterned conductive layer.
[0029] Preferably the laser is of infrared wavelength, such as 834nm or 1064 nm. The use
of infrared light further inhibits the degradation of the underlying layers, as low-energy
infrared light is less likely to induce photochemical changes in any of the active
layers of the electronic device.
[0030] Embodiments of the method are also applicable to laser patterning in the visible
and ultraviolet spectral range provided that care is taken to reduce the leakage of
light to the active layers underneath the conducting layer, as mentioned above.
[0031] In a third class of embodiments of the invention a pixel electrode is defined by
the isolation of electrode pads on a polymer surface by providing a thick dielectric
layer deposited on top of the transistor array. The dielectric layer provided is optically
thick, i.e. has a composition such that the laser light is strongly absorbed in the
dielectric layer and does not irradiate the components of the underlying active elements
with high light intensity. An absorbing dye moiety may be added to the dielectric
layer to increase its optical density at the wavelength of laser light. The stack
may then be irradiated by an infrared or ultraviolet laser beam such that the surface
region of the aforementioned dielectric layer melts or ablates away. The laser beam
does not completely penetrate the layer. The underlying layers are therefore protected.
This step removes conductive material within this conductive layer to remove any conductive
pathways between two adjacent electrode pads resulting in the isolation of the device.
[0032] The dielectric layer is preferably a material with a low heat conductivity, most
preferably a polymer dielectric, such as PMMA, polystyrene of parylene. The low heat
conductivity of the dielectric layer reduces thermal damage to the underlying device
by the absorption of the laser light. Preferably the thermal conductivity of the dielectric
is less than 1.10
-2 W /cm·K.
[0033] In at least the first two classes of embodiments, the process can be self-limiting
in the sense that material is substantially only removed from the light absorbing
layer itself, and from any of the layers above the light absorbing layer, but not
substantially from any of the layers underneath. The underlying layers are not removed
from the substrate or preferably even melted. This can be achieved by selecting the
laser wavelength such that the laser light is not strongly absorbed by any of the
sensitive functional layers of the active electronic device. In the case of infrared
radiation many polymer semiconductors and dielectrics are substantially transparent
to infrared light. Therefore, once the infrared light absorbing layer is ablated or
removed no significant further ablation of underlying material occurs. In addition,
this process has also been shown to produce very little excess debris.
[0034] In all three classes of embodiments the conductive layer can either be an inorganic
metal deposited from vapour or liquid phase or an organic conductor. Most preferable
the conductive material is a solution deposited conducting polymer. Compared to inorganic
metals conducting polymers can be patterned with a lower laser energy. This helps
to avoid degradation of the underlying structure.
[0035] To help understanding of the invention, the invention will now be described by way
of example and with reference to the accompanying drawings, in which:
Figure 1 illustrates a conventional method of producing a multi-level polymer stack.
Figure 2 shows a method for defining the upper pixel electrode on top of a multi-level
pixel structure wherein, an insulating layer underneath the organic conductor layer
contains a moiety which absorbs IR radiation.
Figure 3 shows an absorption spectra for PVP films mixed with various concentrations
(in wt%) of the IR dye SDA4927.
Figure 4 shows images of PVP films mixed with (a) 2.5 wt% and (b) 10wt% IR dye SDA4927
on a blank glass substrate coated with the organic conductor PEDOT/PSS in which organic
electrodes have been isolated by ablating 20 µm wide lines with an IR laser.
Figure 5 illustrates a top view of a multi-level polymer stack with isolated upper
pixel electrodes.
Figure 6 illustrates a method for defining the upper pixel electrode on top of a multi-level
pixel structure wherein an insulating layer with the IR absorbing moiety is separated
from organic conductor by a non-absorbing wetting layer.
Figure 7 illustrates a method for defining the upper pixel electrode on top of a multi-level
pixel structure wherein, a conductive layer is provided with a moiety which absorbs
IR radiation.
Figure 8 illustrates a method of producing a multi-level polymer stack, incorporating
a thick dielectric layer to allow for incomplete penetration by a UV laser beam.
Figure 9 illustrates a method for defining the upper pixel electrode on top of a multi-level
pixel structure wherein, the dielectric layer is irradiated using a UV laser beam.
[0036] Broadly we will describe examples of a method to isolate conductive pads on top of
a multi-layer polymer device structure. The method utilizes laser radiation to ablate
conductive material and create a non-conductive path, electrically isolating the conductive
pads. The process is self-limiting and incorporates at least one layer within the
stack that absorbs the radiation at the required wavelength. The prevention of radiation
degradation of the underlying layers is achieved, as absorption of radiation occurs
primarily on the surface of the structure, but not in any of the radiation sensitive
underlying of the electronic device. The method preferably uses low energy infrared
radiation which has been shown to produce little debris and no device degradation.
Example 1 Direct-write patterning of top conductive electrode
[0037] The fabrication of a multi-level (or -layer) stack for polymer-based printed TFTs
according to a conventional method is illustrated in Figure 1. Conductive material
is deposited and patterned on a substrate 1 to form source and drain electrodes 2.
The substrate may be either glass or a polymer film, but preferably a plastic substrate
such as polyethyleneterephtalate (PET) or polyethylenenaphtalene (PEN) is used. The
patterned conductive layer 2 comprises a conducting polymer, such as PEDOT, or a metallic
material, such as gold or silver. It may be deposited and patterned through solution
processing techniques such as, but not limited to, spin, dip, blade, bar, slot-die,
or spray coating, inkjet, gravure, offset or screen printing, or evaporation, and
photolithography techniques.
[0038] Once the conductive layer has been patterned to form the source and drain electrodes,
a layer of semiconducting material 4 may then be deposited over the substrate and
patterned electrodes. The semiconducting layer may consist of materials such as, but
not limited to, polyarylamine, polyfluorene or polythiophene derivatives. A broad
range of printing techniques may be used to deposit the semiconducting material including,
but not limited to, inkjet printing, soft lithographic printing (
J.A. Rogers et al., Appl. Phys. Lett. 75, 1010 (1999);
S. Brittain et al., Physics World May 1998, p. 31), screen printing (
Z. Bao, et al., Chem. Mat. 9, 12999 (1997)), offset printing, blade coating or dip coating, curtain coating, meniscus coating,
spray coating, or extrusion coating. Alternatively, the semiconducting layer may be
deposited as a thin continuous film and patterned substractively by techniques such
as photolithography (see
WO 99/10939) or laser ablation.
[0039] A layer of gate dielectric material 5 is then deposited onto the layered substrate.
Materials such as polyisobutylene or polyvinylphenol may be used as the dielectric
material, but preferably polymethylmethacrylate (PMMA) and polystyrene are used. The
dielectric material may be deposited in the form of a continuous layer, by techniques
such as, but not limited to, spray or blade coating. However, preferably, the technique
of spray coating is used.
[0040] The deposition of the dielectric layer is then followed by the deposition and patterning
of a gate electrode 6 and interconnect lines. The material of the gate electrode may
be a patterned thin film of inorganic metals such as gold or a pattern of printable
inorganic nanoparticles of silver or gold, or a conducting polymer, such as polyethylenedioxythiophene
doped with polystyrene sulfonic acid (PEDOT/PSS). The gate electrode is deposited
using techniques such as sputtering or evaporation techniques or solution processing
techniques such as spin, dip, blade, bar, slot-die, gravure, offset or screen printing.
Preferably, the gate electrode is deposited using the solution processing technique
of ink jet printing.
[0041] At least one further layer of dielectric material 7 is deposited on the substrate
after the deposition of the gate electrode and interconnect and data lines. The dielectric
material may be deposited from solution in the form of a continuous layer, by techniques
such as, but not limited to, spin coating ink-jet printing, spray-coating, roller
coating spray or blade coating. However, preferably, the technique of spray coating
is used The dielectric material may also be deposited using vapour phase deposition
techniques like evaporation or chemical vapour deposition. The dielectric material
is preferably deposited in such a way so that no degradation occurs to the underlying
layers. A method to achieve this is disclosed in our previous patent application
WO01/47043. In this, a method for forming a transistor was disclosed by depositing a first material
from solution in a first solvent to form a first layer of the transistor; and subsequently
whilst the first material remains soluble in the first solvent, forming a second layer
of the transistor by depositing over the first material a second material from solution
in a second solvent in which the first material is substantially insoluble. A suitable
solution processible dielectric material that may be used as a second dielectric layer
is polystyrene dissolved in xylene. In addition, parylene is an example of a dielectric
material that may be deposited via chemical vapour phase deposition.
[0042] According to a conventional method (Fig. 1) the top level, pixel electrode 9 is deposited
as a patterned film using a direct write printing technique such as inkjet printing
of a conducting polymer. The pixel electrode is connected to the underlying drain
electrode of the TFT through a via hole interconnection 11.
[0043] Techniques for via hole opening and via fabrication, and other selective connection
formation techniques such as selective removal of layers, are described at pages 32
to 39 of
WO 01/47043, with reference to Figures 12 to 15, which material is specifically incorporated
by reference in this application.
[0044] This method has the disadvantage that in order to ensure the high yielding isolation
of neighbouring pixels the distance between neighbouring pixel electrodes cannot be
chosen less than typically 20 µm, which limits the achievable aperture ratio of the
display.
Example 2 Patterning of the top conductive layer using a light absorbing layer
[0045] Figure 2 illustrates a first embodiment of the present invention. In this and later
examples like elements to those of Figure 1 are indicated by like reference numerals.
The top conductive layer for the pixel electrode is defined by the division of conductive
layer to produce separate electrode pads on a polymer surface, and therefore creating
devices with mutually isolated pixel electrode lines. An insulating wetting layer
8, which contains a dye, that absorbs IR radiation, is deposited on top of the second
dielectric 7. The material of the insulating layer may be deposited from solution
in the form of a continuous layer using techniques such as, but not limited to, spincoating,
ink-jet printing, spray-coating, roller coating spray or blade coating. However, preferably,
the technique of spray coating is used As stated above for the dielectric layers,
this insulating layer is deposited in such a way so as to inhibit degradation of the
underlying layers. The insulating layer preferably has a surface energy which provides
good wetting and adhesion for the deposition of an conductive material 9. Preferably
the conductive material is deposited as a thin continuous film by techniques such
as, but not limited to inkjet printing, offset printing, blade coating or dip coating,
curtain coating, meniscus coating, spray coating, or extrusion coating, The top conductive
layer is preferably a conducting polymer such as PEDOT/PSS.
[0046] The stack may be irradiated with an infrared laser beam 10 such that the absorbing
layer melts or ablates away. This step removes a conductive pathway between two adjacent
electrode pads resulting in their isolation. The size of the non-conductive channels
12 produced between the resultant conductive pads is determined by the spot size of
the laser beam.
[0047] An example of the insulating wetting layer 8 and IR absorbing moiety is poly (4-vinylphenol)
(PVP) with the infrared dye SDA4927 added. This mixture is soluble in methanol which
allows it to be processed from solution.
[0048] The optical absorption spectra of 1.3 µm thick films of PVP with various concentrations
of the dye are shown in Figure 3. As an example, 20 µm lines were cut into these films
by irradiating them with an infrared laser with 832 nm radiation. A fluency of 2031
mJ / cm
2 was used for this experiment. Subsequent measurements showed that the depth of the
line varied as a function of dye concentration, with 700 nm deep lines seen in the
film with 10 wt% dye and film and only 250nm gaps deep lines seen in the film with
2.5 wt% dye. The fact that the depth of the line correlates to the concentration of
dye shows how this ablation step can be self-limiting.
[0049] Figure 4 shows images of a stack of an absorbing layer of PVP with 2.5 wt% and 10
wt% SDA4927 and a film of the organic conductor PEDOT/PSS. Isolated electrodes were
formed using the same laser radiation as above. These images show that no excess debris
is formed during this ablation step.
[0050] A PVP film was loaded with SDA4927 and deposited on top of a second dielectric of
a substrate in which an array of multi-level polymer transistors were already fabricated.
After cutting a via hole 11 through all the layers to the drain electrode the panel
was coated with PEDOT/PSS by spin coating.
[0051] Figure 5 shows a top view of a substrate after it was irradiated with 832 nm radiation
with a fluency of 2031 mJ / cm
2 to form 40 µm non-conductive gaps in the PEDOT/PSS layer, showing drain/source electrode
material 2, gate electrode 6, via 11 and laser patterning trenches 12. The laser irradiated
and ablated regions extend over the area of the transistor devices underneath. Nevertheless,
no degradation of the TFT device characteristics upon laser patterning of the top
electrode was observed.
[0052] The process can be seen to result in clean separation of the pixel electrodes without
significant generation of debris or particles in the vicinity of the gap. This is
believed to be due to the large wavelength/small energy of the IR laser beam. Depending
upon laser power, rather than ablating material from the substrate the infrared beam
may only melt the conductive material and/or the light absorbing wetting layer in
the exposed regions, this being followed by de-wetting of the molten material and
subsequent opening of an electrically insulating gap.
[0053] Preferably, the optical density of the IR absorbing layer is higher than 0.3 - 0.5.
Example 3 - Patterning of top conductive layer by using an optically thick dielectric
layer and infrared light
[0054] Figure 6 illustrates a variant of a process based on the first embodiment wherein
the IR absorbing moiety is added to a thick dielectric material. The second dielectric
layer 7, which has an added moiety which absorbs IR radiation, is deposited on top
of gate interconnect 6. The material of the second dielectric layer may be deposited
from solution in the form of a continuous layer using techniques such as, but not
limited to, spincoating, ink-jet printing, spray-coating, roller coating spray or
blade coating. However, preferably, the technique of spray coating is used. The dielectric
material may also be deposited using vapour phase deposition techniques like evaporation
or chemical vapour deposition. As is described above for the first embodiment, and
is referred to in
WO01/47043, the material of the dielectric layer is preferably deposited in such a way so as
to inhibit degradation to the underlying layers. If the second dielectric layer does
not provide good wetting and adhesion for the deposition of the organic conductive
material 9, than an additional insulating / wetting layer 8 can be used to facilitate
the deposition of the layer of organic conductor material. An example of a material
that may be used for the wetting layer is polyvinylphenol. This polymer is soluble
in polar solvents, such as methanol or isopropanol. This layer is preferably thin,
for example in the region of 30nm in order to facilitate patterning of the conductive
layer on top with the laser radiation absorbed in the dielectric layer.
[0055] The stack is irradiated with an infrared laser beam 10 such that the absorbing layer
melts or ablates away. This step removes a conductive pathway 12 between two adjacent
electrode pads resulting in their isolation. An example of a solution processible
dielectric material is polystyrene mixed with a suitable infrared dye (SDA4554). This
mixture is soluble in apolar solvents such as xylene and shows an absorption peak
around 832 nm. When 832 nm radiation source with a fluency of 2031 m J / cm
2 is used for the isolation process, it was found that the optical density of a four
micron film of this material must be greater than 0.5 before significant material
is removed, for other materials/fluences a lower OD may suffice.
Example 4 Patterning of the top conductive layer by using a light absorbing conductive
layer
[0056] In a second embodiment of the invention, as illustrated in Figure 7, a pixel electrode
is defined by the isolation of electrode pads on a polymer surface by providing a
layer of conductive material 9 that contains an IR absorbing moiety. The conductive
material with added IR absorbing moiety is deposited on the top of the layered substrate.
The stack may then be irradiated by an infrared laser beam such that the regions of
the layer containing the absorbing material melts or ablates away. This step removes
any conductive pathways between two adjacent electrode pads resulting in the isolation
of the device.
[0057] When the multi-level stack is irradiated with infrared radiation 10, the conductive
layer is ablated or melted, such that non-conductive channels 12 are formed within
the conductive layer when exposed to infrared radiation. The radiation source 10 is
selected such that it is absorbed by the chemical moieties within the conductive layer.
As stated above, the size of the non-conductive channels between the conductive pads
is determined by the spot size of the laser beam.
[0058] The result of removing material within a conductive layer is achieved by conducting
the aforementioned method as described in the above embodiment. This process may be
carried out without the production of excess debris, which would lead to shorts within
the device.
Example 5 Patterning of the top conductive layer by using an optically thick dielectric
and ultraviolet light
[0059] In the third embodiment of the invention, as illustrated in Figure 8, a pixel electrode
is defined by the isolation of electrode pads on a polymer surface by providing a
thick dielectric layer 7 deposited on top of the gate electrode.
[0060] Referring now to Figure 9, the stack may then be irradiated by an ultraviolet laser
beam such that regions of the aforementioned dielectric layer melts or ablates away.
The wavelength of the ultraviolet laser beam is chosen such that it is absorbed in
the dielectric layer 7. The dielectric layer provided is optically thick, such that
the ultraviolet laser light does not completely penetrate the layer for example less
than 10%, 1% or 0.1% of the light emerging. The underlying layers are therefore protected.
This step removes conductive pathways between two adjacent electrode pads resulting
in the isolation of the device.
[0061] As stated above, the material of the second dielectric layer 7 may be deposited on
top of the gate electrode 6 from solution in the form of a continuous layer using
techniques such as, but not limited to, spincoating, ink-jet printing, spray-coating,
roller coating spray or blade coating. However, preferably, the technique of spray
coating is used The dielectric material may also be deposited using vapour phase deposition
techniques like evaporation or chemical vapour deposition. As is described above for
the first embodiment, and is referred to in our previous patent (
WO01/47043), the material of the dielectric layer should be deposited in such a way so as to
not cause any degradation to the underlying layers. If the second dielectric layer
does not have a surface energy which allows for the deposition of the organic conductive
material 10, than an additional insulating wetting layer 8 can be used to facilitate
the deposition of the organic conductor. An example of this material that may be used
for the wetting layer is polyvinylphenol. A via hole is then made (as described above)
through the multilayered stack to provide an avenue for the upper pixel electrode
to contact to drain electrode of the TFT.
[0062] Preferably the thickness of said dielectric layer is equal to or greater than 1 micron,
in order to reduce laser damage to the underlying organic electronic device during
patterning.
[0063] In this embodiment, an ultraviolet laser 10 is used to ablate through the layer of
organic conductor material and into the second dielectric layer to isolate the top
pixel. As previously stated, solution-processible polystyrene dissolved in xylene
and/or parylene and processed from a chemical vapour phase deposition technique are
suitable for this layer. However, it is important that the second dielectric layer
is thick enough to prevent the ultraviolet radiation from causing significant degradation
to the underlying TFT layers. The conducting material for the top pixel electrode
is preferably a conducting polymer such as PEDOT/PSS which provides efficient absorption
at UV wavelengths (for example 248 run) without having to add a dye component, and
exhibits sufficiently low ablation threshold that degradation of underlying layers
can be minimized. In this way the laser exposure dose can be adjusted such that only
a thin portion of the underlying pixel dielectric is removed when patterning the top
pixel electrode. Preferably the thickness of the pixel dielectric is larger than 3
mm, and the laser ablation of the PEDOT film is preferably performed in a single-shot
exposure from a 248 nm excimer with a 30nm pulse length. Preferably, the single shot
process operates with a fluency between 100-800 mJ/cm
2.
[0064] Embodiments of the invention are applicable to a range of process conditions. For
high laser intensities the conductive layer is ablated from the substrate. For low
and medium laser intensities the conductive layer can only be melted. In the molten
state it can dewet from the substrate causing a break in the conductive path. The
latter process condition can be preferable if generation of debris is to be avoided.
The de-wetting of the conductive material can be encouraged by adjusting the interface
energy between the conductive layer and the underlying layer on the substrate. A high
interface tension will favour de-wetting when the conductive layer is hit by the laser
beam.
[0065] The processes and devices described herein are not limited to devices fabricated
with solution-processed polymers. Some of the conducting electrodes of the TFT and/or
the interconnects in a circuit or display device (see below) may be formed from inorganic
conductors, that can, for example, be deposited by the printing of a colloidal suspension
or by electroplating onto a pre-patterned substrate. In devices where not all of the
layers deposited from solution, one or more PEDOT/PSS portions of the device may be
replaced with an insoluble conductive material such as a vacuum-deposited conductor.
[0066] In particular, the conducting material for the pixel electrode may comprise inorganic
conductor, such as a solution-processible nanoparticle metal, such as gold, or metal
precursor with which higher conductivities can be achieved than with conducting polymers.
Alternatively, a thin film of a vacuum deposited or electroless plated metal can be
used. However, in these cases the thickness of the metal layer is preferably thin,
so as to reduce the laser energy required for patterning/ablation of the metal layer.
Preferably the metal layer thickness is less than 200nm, most preferably, less than
100nm.
[0067] Examples of materials that may be used for the semiconducting layer, include any
solution processible conjugated polymeric or oligomeric material that exhibits adequate
field-effect mobilities exceeding 10
-3 cm
2/Vs and preferably exceeding 10
-2 cm
2/Vs. Materials that may be suitable have been previously reviewed, for example in
H.E. Katz, J. Mater. Chem. 7, 369 (1997), or
Z. Bao, Advanced Materials 12, 227 (2000). Other possibilities include small conjugated molecules with solubilising side chains
(
J.G. Laquindanum, et al., J. Am. Chem. Soc. 120, 664 (1998)), semiconducting organic-inorganic hybrid materials self-assembled from solution
(
C.R. Kagan, et al., Science 286, 946 (1999)), or solution-deposited inorganic semiconductors such as CdSe nanoparticles (
B. A. Ridley, et al., Science 286, 746 (1999)) or inorganic semiconducting nanowires.
[0068] The electrodes may be coarse-patterned by techniques other than inkjet printing.
Suitable techniques include soft lithographic printing (
J.A. Rogers et al., Appl. Phys. Lett. 75, 1010 (1999); S.
Brittain et al., Physics World May 1998, p. 31), screen printing (
Z. Bao, et al., Chem. Mat. 9, 12999 (1997)), and photolithographic patterning (see
WO 99/10939), offset printing, flexographic printing or other graphic arts printing techniques.
However, ink-jet printing is considered to be particularly suitable for large area
patterning with good registration, in particular for flexible plastic substrates.
In the case of surface-energy direct deposition, materials may also be deposited by
continuous film coating techniques such as spin, blade or dip coating, which are then
able to be self-patterned by the surface energy pattern.
[0069] Although preferably all layers and components of the device and circuit are deposited
and patterned by solution processing and printing techniques, one or more components
may also be deposited by vacuum deposition techniques and/or patterned by photolithographic
processes.
[0070] Application of the methods disclosed does not only include patterning of top pixel
electrodes for high aperture ratio active matrix displays. Embodiments can be applied
to any device which requires patterning of a top conductive layer on top of a substrate
which already contains active electronic devices. Examples of this are image sensors,
such as X-ray image sensors, or multilayer interconnects for integrated logic circuits.
Patterning processes, as described above, may also be used to pattern active and passive
devices, for example other circuitry components such as, but not limited to, interconnects,
resistors and capacitors. Similarly, the process can be applied to patterning of electrodes
of devices with underlying sensitive layers, such as gate electrodes in a top-gate
TFT, or source-drain electrodes in a bottom-gate TFT.
[0071] The present invention is not limited to the foregoing examples. Aspects of the present
invention include all novel and inventive aspects of the concepts described herein
and all novel and inventive combinations of the features described herein.
[0072] The applicant hereby discloses in isolation each individual feature described herein
and any combination of two or more such features, to the extent that such features
or combinations are capable of being carried out based on the present specification
as a whole in light of the common general knowledge of a person skilled in the art,
irrespective of whether such features or combinations of features solve any problems
disclosed herein. The applicant indicates that aspects of the present invention may
consist of any such individual feature or combination of features. In view of the
foregoing description it will be evident to a person skilled in the art that various
modifications may be made within the scope of the invention as set out in the claims
1. A method of patterning a top conductive layer (9) on a substrate containing an array
of active electronic devices to form pixel electrodes for the array of electronic
devices in a multilayer device structure, the method comprising:
depositing a layer of insulating dielectric material on the active electronic devices
to provide a dielectric layer (7); and
depositing a layer of conducting material over the dielectric material to provide
the top conductive layer(9);
wherein the dielectric layer (7), or a separate layer (8) under the top conductive
layer (7) comprises a light absorbing material;
the method
characterised by:
irradiating portions of the substrate with laser light, whereby portions of the top
conductive layer (9) are selectively removed by melting or ablation from said Irradiated
substrate portions, the laser light being of a wavelength absorbed by said light absorbing
material, whereby significant degradation of the underlying array of active electronic
devices is prevented, and
the dielectric layer (7) remaining under the pixel electrodes as part of the multilayer
device structure.
2. A method as claimed in claim 1 wherein said light absorbing material comprises a dye.
3. A method as claimed in claim 1 or claim 2 wherein said conducting material comprises
a conducting polymer.
4. A method as claimed in any of claims 1 to 3 wherein said light comprises ultraviolet
light.
5. A method as claimed any one of claims 1 to 4, wherein said dielectric material comprises
a polymer dielectric.
6. A method as claimed in any one of claims 1 to 5 wherein the insulating dielectric
material provides said light absorbing material.
7. A method as claimed in claim 6 wherein the thickness of said dielectric layer (7)
is greater than 1 micron.
8. A method as claimed in claim 7 wherein the thickness of said dielectric layer (7)
is greater than 3 microns.
9. A method as claimed in any one of claims 1 to 5 comprising depositing a separate layer
(8) of said light absorbing material prior to depositing said layer of conducting
material, whereby said separate layer (8) of light absorbing material is under said
top conductive layer (9).
10. A method as claimed in any preceding claim wherein said light absorbing material has
an optical density of at least 0.3 at a wavelength of the light.
11. A method as claimed in claim 11 wherein said light absorbing material has an optical
density of at least 0.5 at a wavelength of the light.
12. A method as claimed in any preceding claim wherein said dielectric layer (7) has a
thermal conductivity of less than 10-2 W/cm.K.
13. A method as claimed in any one of claims 1 to 12, the method further comprising providing
a wetting interface or layer (8) beneath said top conductive layer (9).
14. A method as claimed in any one of claims 1 to 12, the method further comprising providing
a de-wetting interface or layer (8) beneath said top conductive layer (9).
15. A method as claimed in any preceding claim wherein said selective removal is self-limiting,
whereby only light absorbing material and material above this are removed.
16. A method of fabricating an active matrix display or image sensor, the method comprising:
forming a pixel electrode layer by patterning a top conductive layer (9) on a substrate
for the active matrix display or image sensor using the method of any preceding claim,
wherein the active electronic devices are thin film transistors; and
fabricating said active matrix display or image sensor using said substrate with said
pixel electrode layer.
1. Verfahren zum Strukturieren einer oberen Leitschicht (9) auf einem Substrat, enthaltend
eine Anordnung von aktiven elektronischen Vorrichtungen, um Pixelelektroden für die
Anordnung von elektronischen Vorrichtungen in einer mehrschichtigen Vorrichtungsstruktur
zu bilden, wobei das Verfahren umfasst:
Vorsehen einer Schicht aus dielektrischem Isoliermaterial auf den aktiven elektronischen
Vorrichtungen, um eine dielektrische Schicht (7) bereitzustellen; und
Vorsehen einer Schicht aus Leitmaterial über dem dielektrischen Material, um die obere
Leitschicht (9) bereitzustellen;
wobei die dielektrische Schicht (7) oder eine separate Schicht (8) unter der oberen
Leitschicht (7) ein lichtabsorbierendes Material umfasst;
wobei das Verfahren
gekennzeichnet ist:
durch Bestrahlen von Teilen des Substrats mit Laserlicht, wobei Teile der oberen Leitschicht
(9) durch Schmelzen oder Ablation selektiv von den bestrahlten Substratteilen entfernt
werden, wobei das Laserlicht eine Wellenlänge aufweist, die vom lichtabsorbierenden
Material absorbiert wird, wobei ein signifikanter Abbau der zugrundeliegenden Anordnung
von aktiven elektronischen Vorrichtungen verhindert wird, und
dadurch, dass die dielektrische Schicht (7) unter den Pixelelektroden als Teil der mehrschichtigen
Vorrichtungsstruktur bleibt.
2. Verfahren nach Anspruch 1, wobei das lichtabsorbierende Material einen Farbstoff umfasst.
3. Verfahren nach Anspruch 1 oder 2, wobei das Leitmaterial ein leitfähiges Polymer umfasst.
4. Verfahren nach einem der Ansprüche 1 bis 3, wobei das Licht ultraviolettes Licht umfasst.
5. Verfahren nach einem der Ansprüche 1 bis 4, wobei das dielektrische Material ein Polymerdielektrikum
umfasst.
6. Verfahren nach einem der Ansprüche 1 bis 5, wobei das dielektrische Isoliermaterial
das lichtabsorbierende Material bereitstellt.
7. Verfahren nach Anspruch 6, wobei die Dicke der dielektrischen Schicht (7) größer als
1 µm ist.
8. Verfahren nach Anspruch 7, wobei die Dicke der dielektrischen Schicht (7) größer als
3 µm ist.
9. Verfahren nach einem der Ansprüche 1 bis 5, umfassend das Vorsehen einer separaten
Schicht (8) des lichtabsorbierenden Materials vor dem Vorsehen der Leitmaterialschicht,
wobei sich die separate Schicht (8) aus lichtabsorbierendem Material unter der oberen
Leitschicht (9) befindet.
10. Verfahren nach einem vorstehenden Anspruch, wobei das lichtabsorbierende Material
eine optische Dichte von zumindest 0,3 bei einer Wellenlänge des Lichts aufweist.
11. Verfahren nach Anspruch 11, wobei das lichtabsorbierende Material eine optische Dichte
von zumindest 0,5 bei einer Wellenlänge des Lichts aufweist.
12. Verfahren nach einem vorstehenden Anspruch, wobei die dielektrische Schicht (7) eine
Wärmeleitfähigkeit von weniger als 10-2 W/cm.K aufweist.
13. Verfahren nach einem der Ansprüche 1 bis 12, wobei das Verfahren ferner das Vorsehen
einer Benetzungsgrenzfläche (8) unterhalb der oberen Leitschicht (9) umfasst.
14. Verfahren nach einem der Ansprüche 1 bis 12, wobei das Verfahren ferner das Vorsehen
einer Entnetzungsgrenzfläche (8) unterhalb der oberen Leitschicht (9) umfasst.
15. Verfahren nach einem vorstehenden Anspruch, wobei das selektive Auswählen selbstbegrenzend
ist, wobei nur lichtabsorbierendes Material und Material über diesem entfernt werden.
16. Verfahren zum Herstellen eines Active-Matrix-Displays oder -Bildsensors, wobei das
Verfahren umfasst:
Bilden einer Pixelelektrodenschicht durch Strukturieren einer oberen Leitschicht (9)
auf einem Substrat für das Active-Matrix-Display oder den Active-Matrix-Bildsensor
unter Verwendung des Verfahrens nach einem vorstehenden Anspruch, wobei die aktiven
elektronischen Vorrichtungen Dünnschichttransistoren sind;
und
Herstellen des Active-Matrix-Displays oder -Bildsensors unter Verwendung des Substrats
mit der Pixelelektrodenschicht.
1. Procédé de modelage d'une couche conductrice supérieure (9) sur un substrat contenant
un réseau de dispositifs électroniques actifs pour former des électrodes de pixel
pour le réseau de dispositifs électroniques dans une structure de dispositifs multicouche,
le procédé comprenant :
le dépôt d'une couche de matériau diélectrique isolant sur les dispositifs électroniques
actifs pour former une couche diélectrique (7) ; et
le dépôt d'une couche de matériau conducteur sur le matériau diélectrique pour former
la couche conductrice supérieure (9) ;
dans lequel la couche diélectrique (7) ou une couche séparée (8) sous la couche conductrice
supérieure (7) comprend un matériau absorbant la lumière ;
le procédé étant
caractérisé par :
l'irradiation de parties du substrat avec une lumière laser, de telle manière que
des parties de la couche conductrice supérieure (9) soient sélectivement enlevées
par fusion ou ablation desdites parties de substrat irradiées, la lumière laser étant
d'une longueur d'onde absorbée par ledit matériau absorbant la lumière, de telle manière
qu'une dégradation significative du réseau sous-jacent de dispositifs électroniques
actifs soit prévenue, et
la couche diélectrique (7) restant sous les électrodes de pixel en tant que partie
de la structure de dispositif muticouche.
2. Procédé selon la revendication 1 dans lequel ledit matériau absorbant la lumière comprend
un colorant.
3. Procédé selon la revendication 1 ou la revendication 2 dans lequel ledit matériau
conducteur comprend un polymère conducteur.
4. Procédé selon l'une quelconque des revendications 1 à 3 dans lequel ladite lumière
comprend une lumière ultraviolette.
5. Procédé selon l'une quelconque des revendications 1 à 4, dans lequel ledit matériau
diélectrique comprend un polymère diélectrique.
6. Procédé selon l'une quelconque des revendications 1 à 5 dans lequel le matériau diélectrique
isolant constitue ledit matériau absorbant la lumière.
7. Procédé selon la revendication 6 dans lequel l'épaisseur de ladite couche diélectrique
(7) est supérieure à 1 micron.
8. Procédé selon la revendication 7 dans lequel l'épaisseur de ladite couche diélectrique
(7) est supérieure à 3 microns.
9. Procédé selon l'une quelconque des revendications 1 à 5 comprenant le dépôt d'une
couche séparée (8) dudit matériau absorbant la lumière avant le dépôt de ladite couche
de matériau conducteur, de telle manière que ladite couche séparée (8) de matériau
absorbant la lumière soit sous ladite couche conductrice supérieure (9).
10. Procédé selon l'une quelconque des revendications précédentes dans lequel ledit matériau
absorbant la lumière a une densité optique d'au moins 0,3 à une longueur d'onde de
la lumière.
11. Procédé selon la revendication 11 dans lequel ledit matériau absorbant la lumière
a une densité optique d'au moins 0,5 à une longueur d'onde de la lumière.
12. Procédé selon l'une quelconque des revendications précédentes dans lequel ladite couche
diélectrique (7) a une conductivité thermique inférieure à 10-2 W/cm.K.
13. Procédé selon l'une quelconque des revendications 1 à 12, le procédé comprenant en
outre la formation d'une interface ou couche de mouillage (8) au-dessous de ladite
couche conductrice supérieure (9).
14. Procédé selon l'une quelconque des revendications 1 à 12, le procédé comprenant en
outre la formation d'une interface ou couche de démouillage (8) au-dessous de ladite
couche conductrice supérieure (9).
15. Procédé selon l'une quelconque des revendications précédentes dans lequel ladite élimination
sélective est autolimitante, de telle manière que seul le matériau absorbant la lumière
et le matériau au-dessus de celui-ci soient enlevés.
16. Procédé de fabrication d'un affichage ou capteur d'image à matrice active, le procédé
comprenant :
la formation d'une couche d'électrodes de pixel par modelage d'une couche conductrice
supérieure (9) sur un substrat pour l'affichage ou capteur d'image à matrice active
en utilisant le procédé de l'une quelconque des revendications précédentes, dans lequel
les dispositifs électroniques actifs sont des transistors à couche mince ; et
la fabrication dudit affichage ou capteur d'image à matrice active en utilisant ledit
substrat avec ladite couche d'électrodes de pixel.